Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

964
FXUS63 KLOT 201115
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
615 AM CDT Wed May 20 2026

.KEY MESSAGES...

- Dry but cooler conditions today and Thursday, followed by
  increasing rain chances Friday.

- Intermittent shower/thunderstorm chances for Memorial Day
  weekend, though much of the period should be dry.

- Several periods of moderate to high swim risk conditions
  possible from today through early next week due to persistent
  northeast winds over Lake Michigan.

&&

.DISCUSSION...
Issued at 314 AM CDT Wed May 20 2026

Mainly dry, breezy and cooler weather conditions are expected
today through Thursday, in the wake of yesterday`s cold frontal
passage. Early morning surface analysis shows this front now
extends from western Lake Erie to far southern Illinois along
the Ohio River. Have noted a few spotty sprinkles as far north
as the Pontiac-Rensselaer areas overnight, likely where
lingering moist advection was still occurring within the
elevated baroclinic zone north of the surface front. These will
end prior to sunrise however, as the southern periphery of a
mid-level short wave trough passes east of the region. Farther
northwest, 1026 mb surface high pressure was centered near Sioux
Falls this morning, and is progged to build east-northeast
across the upper Great Lakes region by tonight. This will result
in our north-northwest winds shifting northeast and becoming
breezy by midday/afternoon with gusts near 20 mph (around 25 mph
near/downwind of Lake Michigan into northeast IL/northwest IN).
Temperatures, after being in the 70s and 80s over the past
several days, will be limited to the low-mid 50s along the Lake
Michigan shore, and the low-mid 60s well inland beneath partly
to mostly cloudy skies. With the breezy northeast winds and
building waves on the lake, have issued a Beach Hazard Statement
for the Illinois and Indiana shores today into Thursday.

Overnight lows tonight may dip to around the 40 degree mark
along the IL/WI border, and in the low-mid 40s elsewhere with
partly cloudy skies. Thursday will be similar, though with more
easterly winds and slightly milder temperatures in the mid-upper
60s well west and south of the lake-cooled areas of northeast
IL and far northwest IN.

Clouds look to spread in from the west late Thursday/Thursday
night, ahead of a mid-level short wave lifting northeast from
the southern Plains and the base of a western CONUS upper
trough. An associated surface low pressure wave is progged to
track into the lower Missouri Valley by late Thursday night,
then slowly track northeast across central IL/northern IN Friday
into Friday night as the short wave transits the region. This
is expected to spread rain/showers across the area during this
time, though there remains some guidance/ensemble spread as to
the northward extent of the rain shield into our antecedent dry
low-level air, though rain chances increase across much of the
area by Friday afternoon and evening. Thunder potential looks
quite low, with the forecast MUCAPE reservoir forecast to remain
largely south of the cwa. Cloud cover, rain and enhanced E-NE
surface winds north of the low track will make for another cool
day Friday with highs again in the 50s near the lake and low-mid
60s elsewhere. Rain should taper off overnight Friday night as
the mid-level and surface waves pass.

Medium-range ensembles depict the aforementioned western upper
trough tracking slowly across the Midwest through Sunday,
eventually shifting east of the region Monday/Tuesday. While
this may maintain at least some threat of intermittent showers
over the holiday weekend, current guidance suggests that there will
likely be many dry daytime hours. A gradual warming trend is
also depicted Saturday into Tuesday with daytime temperatures
forecast to warm back into the 70s/possibly 80s.

Ratzer

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 615 AM CDT Wed May 20 2026

No major forecast concerns for the terminals through this TAF
period.

High pressure is starting to build in from the northwest which
is scattering clouds across the area. However, a plume of
3000-3500 ft clouds is oozing inland off of southern Lake
Michigan and is impacting ORD, MDW, and GYY. With the increasing
subsidence and high May sun angle, suspect these clouds should
begin to erode over the next 1-2 hours resulting in SCT to BKN
20000-25000 ft clouds for the rest of the period. Though, cannot
rule out that the lower clouds linger through 15z (especially
at GYY) given the developing onshore winds.

Speaking of winds, expect directions to settle into a
northeasterly direction by 13z and will remain as such for the
rest of the period. Speeds will generally be in the 10-15 kt
range today, but some lower 20 kt gusts may be seen at times.
Winds speeds will ease this evening into the 8-10 kt range where
they will remain through the day on Thursday.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement from 1 PM CDT this afternoon through
     Thursday afternoon for ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement through Thursday morning for INZ001.

     Beach Hazards Statement through Thursday morning for INZ002.

LM...Small Craft Advisory from 10 AM this morning to 1 PM CDT
     Thursday for the IL nearshore waters.

     Small Craft Advisory until 7 AM CDT Thursday for the IN
     nearshore waters.

&&

$$

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